Time Synchronization Device, Communication System, and Time Synchronization Method

Abstract

The time synchronization device is the first device. The first device measures the transmission delay time between the second device via a relay device capable of connecting multiple first devices. The time synchronization device includes: a frame transmission unit (32) that sends a request message for measuring the transmission delay time to the second device; a frame reception unit (31) that receives a response message, which is a response to the request message; and a reception monitoring unit (34) that has a reception monitoring timer (340). When the frame transmission unit (32) sends the request message, the reception monitoring timer (340) is started. When the reception monitoring timer (340) times out before the frame reception unit (31) receives the response message, the frame transmission unit (32) is instructed to retransmit the request message. The timeout setting value of the reception monitoring timer (340) is set to tO, the number of connected time synchronization devices to the relay device is set to N, and the transmission period of the request message of the frame transmission unit (32) is set to T, where tO ≤ T / N.

Description

Technical Field

[0001] The present invention relates to a time synchronization device, a communication system, and a time synchronization method for performing time synchronization. Background Art

[0002] Conventionally, in a system in which a plurality of devices connected via a network cooperate to operate, in order to make the control timings of the plurality of devices coincide, it is necessary to synchronize the times of the respective devices. As a standard for time synchronization between devices, there is a time synchronization technique (Non-Patent Document 1) such as IEEE (The Institute of Electrical and Electronics Engineers) 1588, that is, in a master-slave system composed of a plurality of devices, the times of the plurality of devices on the network are synchronized.

[0003] In IEEE 1588, it is stipulated to measure the communication delay time of the transmission path between devices to perform time synchronization. Each device measures the communication delay time of the transmission path at a fixed cycle. The communication delay measurement of the transmission path is implemented by a device that requests the delay measurement, i.e., a Requester, sending a DelayReq message, and a device that receives the DelayReq message, i.e., a Responder, storing the timestamp at the time of receiving the DelayReq in a DelayResp message and sending it to the Requester.

[0004] Non-Patent Document 1: IEEE Std 1588-2008 (IEEE Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems) Summary of the Invention

[0005] However, in a system where there is a switching hub that does not support IEEE 1588 and multiple requesters are connected to the switching hub that does not support IEEE 1588, one responder receives multiple DelayReq messages sent by multiple requesters that perform transmission delay time measurement. The responder needs to save the timestamps when receiving multiple DelayReq messages for each source, but there is a limit to the number of timestamps that can be saved. The responder only sends DelayResp messages to the requesters that have successfully saved the timestamps. Therefore, there is a problem that in a certain cycle, some requesters may not be able to receive DelayResp messages and cannot complete the transmission delay time measurement. In addition, each requester sends DelayReq messages at a fixed cycle. Therefore, there is a problem that a certain requester may not be able to receive DelayResp messages in the next cycle either, cannot complete the transmission delay time measurement, and cannot perform time synchronization.

[0006] The present invention is proposed in view of the above problems, and its object is to obtain a time synchronization device that can perform time synchronization even in a communication system where multiple time synchronization devices are connected to a relay device.

[0007] To solve the above problems and achieve the object, the time synchronization device of the present invention is a first device, and the first device performs transmission delay time measurement between the second device via a relay device that can connect multiple first devices. The time synchronization device has: a sending unit that sends a request message for transmission delay time measurement to the second device; a receiving unit that receives a response message from the second device, which is a response to the request message; and a reception monitoring unit that has a reception monitoring timer, starts the reception monitoring timer when the sending unit sends the request message, and when the reception monitoring timer times out before the receiving unit receives the response message, instructs the sending unit to retransmit the request message. It is characterized in that the timeout setting value of the reception monitoring timer is set to tO, the number of connected time synchronization devices connected to the relay device is set to N, the transmission cycle of the request message of the sending unit is set to T, and tO ≤ T / N.

[0008] Effect of the Invention

[0009] The time synchronization device according to the present invention achieves the effect that time synchronization can also be performed in a communication system where multiple time synchronization devices are connected to a relay device. Description of the Drawings

[0010] Figure 1 It is a diagram showing a structural example of the communication system according to Embodiment 1.

[0011] Figure 2 It is a diagram showing another structural example of the communication system according to Embodiment 1.

[0012] Figure 3 It is a diagram showing a structural example of the synchronous slave station related to Embodiment 1.

[0013] Figure 4 It is a flowchart showing the monitoring operation of the reception monitoring unit of the synchronous slave station related to Embodiment 1.

[0014] Figure 5 It is a timing diagram showing the transmission and reception timings of messages of each device when the synchronous slave station measures the transmission delay time in the communication system related to Embodiment 1.

[0015] Figure 6 It is a diagram showing an example of the hardware that implements the synchronous slave station related to Embodiment 1.

[0016] Figure 7 It is a diagram showing a structural example of the communication system related to Embodiment 2.

[0017] Figure 8 It is a diagram showing another structural example of the communication system related to Embodiment 2.

[0018] Figure 9 It is a diagram showing a structural example of the synchronous slave station related to Embodiment 2.

[0019] Figure 10 It is a flowchart showing the operation of the reception monitoring unit of the synchronous slave station related to Embodiment 2 for calculating the timeout setting value. Detailed Embodiment

[0020] Hereinafter, the time synchronization device, communication system, and time synchronization method related to the embodiments of the present invention will be described in detail based on the accompanying drawings. In addition, the present invention is not limited to this embodiment.

[0021] Embodiment 1.

[0022] Figure 1 It is a diagram showing a structural example of the communication system 4 related to Embodiment 1 of the present invention. The communication system 4 includes: a synchronous master station 1 having a reference time; a switching hub 2 that does not support IEEE 1588; and synchronous slave stations 3a and 3b that are synchronized with the synchronous master station 1. In Figure 1In the communication system 4 shown, the synchronization slave stations 3a and 3b are the requesters for measuring the transmission delay time of the transmission path between them and the synchronization master station 1, and the synchronization master station 1 is the responder. The synchronization master station 1 performs the same actions as the IEEE 1588 standard. When the synchronization master station 1 receives the DelayReq message for measuring the transmission delay time sent from the synchronization slave stations 3a and 3b, it sends the DelayResp message, which is the response to the DelayReq message. The switching hub 2 that does not support IEEE 1588 is a relay device that forwards frames according to the destination address of the received frames. The switching hub 2 can also be connected to three or more synchronization slave stations. The synchronization slave stations 3a and 3b perform the measurement of the transmission delay time with the synchronization master station 1 via the switching hub 2. In the following description, the requester is sometimes referred to as the first device, and the responder is sometimes referred to as the second device. In addition, the requester, i.e., the first device, is sometimes referred to as the time synchronization device.

[0023] In addition, depending on the structure of the communication system, the synchronization slave station may also be the responder. Figure 2 FIG. is a diagram showing a structural example of the communication system 4a according to Embodiment 1. The communication system 4a includes a synchronization master station 1, a switching hub 2, a synchronization slave station 3c, and synchronization slave stations 3a and 3b that are synchronized with the synchronization slave station 3c. In Figure 2 In the communication system 4a shown, the synchronization slave stations 3a and 3b are the requesters for measuring the transmission delay time of the transmission path between them and the synchronization slave station 3c, and the synchronization slave station 3c is the responder. In Figure 2 In the communication system 4a shown, the synchronization slave station 3c can measure the transmission delay time of the transmission path between it and the synchronization master station 1 according to the IEEE 1588 procedure. In the present embodiment, the communication system 4 shown in Figure 1 is taken as an example for description.

[0024] The structure of the synchronization slave stations 3a and 3b will be described. Figure 3 FIG. is a diagram showing a structural example of the synchronization slave station 3a according to Embodiment 1. Since the synchronization slave stations 3a and 3b have the same structure, the synchronization slave station 3a will be taken as an example for description. The synchronization slave station 3a includes a frame receiving unit 31, a frame transmitting unit 32, a time synchronization unit 33, and a reception monitoring unit 34.

[0025] The frame receiving unit 31 is a receiving unit having a frame parsing unit 310. The frame parsing unit 310 parses the frame received from the switching hub 2. When the received frame is a message associated with time synchronization, the frame parsing unit 310 outputs the received data included in the received frame to the time synchronization unit 33. When the synchronization slave station 3a is the requester, if the frame parsing unit 310 receives a DelayResp message targeted at the synchronization slave station 3a among the messages associated with time synchronization, it notifies the reception monitoring unit 34 of the reception of the DelayResp message. The DelayResp message is a message in which the synchronization master station 1 as the responder responds to the DelayReq message received from the synchronization slave station 3a as the requester. In the following description, the DelayResp message may sometimes be referred to as the response message. In addition, the DelayReq message is a message in which the synchronization slave station 3a as the requester requests the synchronization master station 1 as the responder to measure the transmission delay time. In the following description, the DelayReq message may sometimes be referred to as the request message.

[0026] When the synchronization slave station 3a is the responder, if the frame parsing unit 310 receives a DelayReq message among the messages associated with time synchronization, it saves the timestamp value at the reception time point. The frame parsing unit 310 notifies the frame transmission unit 32 of the saved timestamp value, the source information of the DelayReq message indicating the source, i.e., the requester, included in the DelayReq message, and the reception of the DelayReq message.

[0027] The frame transmission unit 32 is a transmission unit having a transmission cycle timer 320. The transmission cycle timer 320 is a timer that times out with the transmission cycle T of the frame transmission unit 32 for transmitting the DelayReq message as the timeout condition. When the synchronization slave station 3a is the requester, if the transmission cycle timer 320 times out after passing the transmission cycle T, the frame transmission unit 32 transmits the DelayReq message to the switching hub 2 at the time of timeout. If the frame transmission unit 32 transmits the DelayReq message, it notifies the time synchronization unit 33 and the reception monitoring unit 34 of the transmission of the DelayReq message. In addition, if the frame transmission unit 32 receives a retransmission instruction for the DelayReq message from the reception monitoring unit 34, it transmits the DelayReq message and restarts the transmission cycle timer 320.

[0028] When the synchronization slave station 3a is the responder, if the frame transmission unit 32 is notified of the timestamp value, the source information of the DelayReq message, and the reception of the DelayReq message from the frame receiving unit 31, it stores the timestamp value and the source information of the DelayReq message in the DelayResp message and transmits it.

[0029] The time synchronization unit 33 has a time counter 330. When the time synchronization unit 33 obtains received data from the frame receiving unit 31, it records the time count value of the time counter 330 at the obtained time point. When the time synchronization unit 33 is notified by the frame transmitting unit 32 that the DelayReq message has been sent, it records the time count value of the time counter 330 at the notified time point. The time synchronization unit 33 calculates the time of the synchronization master station 1 using the recorded time count value and the received data obtained from the frame receiving unit 31, and synchronizes the time counter 330 with the synchronization master station 1.

[0030] For example, let the time when the DelayReq message is sent by the frame transmitting unit 32 be t1, the time when the DelayReq message is received by the synchronization master station 1 be t2, the time when the DelayResp message is sent by the synchronization master station 1 be t3, and the time when the DelayResp message is received by the frame receiving unit 31 be t4. The synchronization master station 1 includes the information of t2 and t3 in the DelayResp message, so that the synchronization slave station 3a can obtain the information of t2 and t3. The time synchronization unit 33 calculates the one-way communication delay time according to ((t4 - t3) + (t2 - t1)) / 2, calculates the time of the synchronization master station 1 using the calculated one-way communication delay time, and synchronizes the time counter 330 with the synchronization master station 1.

[0031] The reception monitoring unit 34 has a reception monitoring timer 340. The reception monitoring timer 340 is a timer for monitoring the reception of the DelayResp message. The reception monitoring unit 34 starts the reception monitoring timer 340 when the frame transmitting unit 32 sends the DelayReq message. When the reception monitoring timer 340 times out before the frame receiving unit 31 receives the DelayResp message, the reception monitoring unit 34 instructs the frame transmitting unit 32 to retransmit the DelayReq message. If the timeout setting value of the reception monitoring timer 340 is set to tO, the number of connections of the requestors (i.e., the synchronization slave stations 3a and 3b) connected to the switching hub 2 is set to N, and the transmission period of the DelayReq message sent by the frame transmitting unit 32 is set to T, then the timeout setting value tO is a value of tO ≤ T / N. Regarding the timeout setting value tO, for example, a user who manages the communication system 4 will preset the result obtained by calculating a value that becomes tO ≤ T / N in the reception monitoring unit 34.

[0032] Next, the operations of the synchronization slave stations 3a and 3b will be described. Figure 4 It is a flowchart showing the monitoring operation of the reception monitoring unit 34 of the synchronization slave station 3a according to Embodiment 1. Since the synchronization slave stations 3a and 3b perform the same operations, the synchronization slave station 3a will be taken as an example for description.

[0033] The reception monitoring unit 34 confirms whether there is a notification indicating that the DelayReq message has been sent from the frame transmission unit 32 (step S11). When there is no notification indicating that the DelayReq message has been sent from the frame transmission unit 32 (step S11: No), the reception monitoring unit 34 stands by until there is a notification indicating that the DelayReq message has been sent from the frame transmission unit 32. When there is a notification indicating that the DelayReq message has been sent from the frame transmission unit 32 (step S11: Yes), the reception monitoring timer 340 is started (step S12).

[0034] If the reception monitoring timer 340 is started, the reception monitoring unit 34 confirms the timeout of the reception monitoring timer 340 (step S13). When the reception monitoring timer 340 has timed out (step S13: Yes), the frame transmission unit 32 is instructed to retransmit the DelayReq message (step S14).

[0035] When the reception monitoring timer 340 has not timed out (step S13: No), the reception monitoring unit 34 confirms whether there is a notification indicating that the DelayResp message has been received from the frame reception unit 31 (step S15). When there is a notification indicating that the DelayResp message has been received from the frame reception unit 31 (step S15: Yes), the reception monitoring timer 340 is stopped and reset (step S16). When there is no notification indicating that the DelayResp message has been received from the frame reception unit 31 (step S15: No), the operation returns to step S13 to confirm the timeout of the reception monitoring timer 340 (step S13).

[0036] The timing of message transmission and reception of each device during the measurement of the transmission delay time at the synchronous slave stations 3a and 3b will be described. Figure 5 It is a timing chart showing the timing of message transmission and reception of each device during the measurement of the transmission delay time at the synchronous slave stations 3a and 3b in the communication system 4 according to the first embodiment. Here, the response party, i.e., the synchronous master station 1, can only save one timestamp value when receiving the DelayReq message.

[0037] The request parties, i.e., the synchronous slave stations 3a and 3b, send the DelayReq message in order to perform the transmission delay time measurement. If the DelayReq message is sent, the synchronous slave stations 3a and 3b start the transmission cycle timer 320 and the reception monitoring timer 340 (step S21).

[0038] In Figure 5In the subsequent description of the timing diagram shown, the DelayReq message sent by the synchronous slave station 3a is set as the DelayReq message 3a, the DelayReq message sent by the synchronous slave station 3b is set as the DelayReq message 3b, the DelayResp message sent from the synchronous master station 1 to the synchronous slave station 3a is set as the DelayResp message 3a, and the DelayResp message sent from the synchronous master station 1 to the synchronous slave station 3b is set as the DelayResp message 3b.

[0039] The responder, i.e., the synchronous master station 1, first receives the DelayReq message 3b from the synchronous slave station 3b and saves the timestamp at the time of reception. The synchronous master station 1 ignores the DelayReq message 3a from the synchronous slave station 3a received immediately thereafter. The synchronous master station 1 sends the DelayResp message 3b to the synchronous slave station 3b (step S22). If the synchronous slave station 3b receives the DelayResp message 3b, it stops and resets the reception monitoring timer 340 (step S23).

[0040] Due to the timeout of the reception monitoring timer 340, the synchronous slave station 3a retransmits the DelayReq message 3a and restarts the transmission cycle timer 320 (step S24). The synchronous master station 1 receives the DelayReq message 3a from the synchronous slave station 3a and saves the timestamp at the time of reception. The synchronous master station 1 sends the DelayResp message 3a to the synchronous slave station 3a (step S25). If the synchronous slave station 3a receives the DelayResp message 3a, it stops and resets the reception monitoring timer 340 (step S26).

[0041] If the transmission cycle timer 320 times out, the synchronous slave station 3b sends the DelayReq message 3b. If the DelayReq message 3b is sent, the synchronous slave station 3b starts the transmission cycle timer 320 and the reception monitoring timer 340 (step S27). The synchronous master station 1 receives the DelayReq message 3b from the synchronous slave station 3b and saves the timestamp at the time of reception. The synchronous master station 1 sends the DelayResp message 3b to the synchronous slave station 3b (step S28). If the synchronous slave station 3b receives the DelayResp message 3b, it stops and resets the reception monitoring timer 340 (step S29).

[0042] If the transmission cycle timer 320 times out, the synchronization slave station 3a sends a DelayReq message 3a. If the DelayReq message 3a is sent, the synchronization slave station 3a starts the transmission cycle timer 320 and the reception monitoring timer 340 (step S30). The synchronization master station 1 receives the DelayReq message 3a from the synchronization slave station 3a and saves the timestamp at the time of reception. The synchronization master station 1 sends a DelayResp message 3a to the synchronization slave station 3a (step S31). If the synchronization slave station 3a receives the DelayResp message 3a, it stops and resets the reception monitoring timer 340 (step S32).

[0043] Thereafter, in the communication system 4, the operations of steps S27 to S32 are repeated. Thus, when the synchronization slave station 3a sends a DelayReq message due to the timeout of the reception monitoring timer 340, it is possible to prevent the transmission timing from overlapping with that of the synchronization slave station 3b whose transmission cycle timer 320 is in the timeout waiting state when sending a DelayReq message. For the synchronization slave station 3a, since the transmission timing of the DelayReq message does not overlap with that of the synchronization slave station 3b, it is possible to complete the transmission delay time measurement and perform time synchronization.

[0044] In the communication system 4, even when the number N of connection requests of the synchronization slave stations connected to the switching hub 2 is greater than or equal to 3, by setting tO ≤ T / N, the transmission timing of the DelayReq message does not overlap between the synchronization slave stations that have completed the transmission delay time measurement and those that have not. As a result, in the communication system 4, all synchronization slave stations can complete the transmission delay time measurement and perform time synchronization.

[0045] Next, the hardware structure of the synchronization slave station 3a will be described. Since the synchronization slave stations 3a and 3b have the same structure, the synchronization slave station 3a will be used for the description. Figure 6 FIG. is an example showing the hardware that implements the synchronization slave station 3a according to Embodiment 1. The synchronization slave station 3a can be implemented by Figure 6 the processor 101, the storage device 102, and the communication interface 103 shown.

[0046] The processor 101 is a CPU (Central Processing Unit, also known as a central processing unit, processing unit, arithmetic unit, microprocessor, microcomputer, DSP (Digital Signal Processor)), a system LSI (Large Scale Integration), etc. The storage device 102 is a RAM (Random Access Memory), ROM (Read Only Memory), EPROM (Erasable Programmable Read Only Memory), EEPROM (registered trademark) (Electrically Erasable Programmable Read Only Memory), a hard disk drive, etc. The communication interface 103 is a processing circuit for receiving a communication frame by the frame receiving unit 31 and transmitting a communication frame by the frame transmitting unit 32 in the synchronous slave station 3a, and is, for example, a network interface card.

[0047] In the synchronous slave station 3a, parts other than the functions implemented by the communication interface 103 in the time synchronization unit 33, the reception monitoring unit 34, the frame receiving unit 31, and the frame transmitting unit 32 are implemented by the processor 101 executing a program for operating as each of the above functional units. Such a program is stored in the storage device 102 in advance. The processor 101 reads and executes the above program from the storage device 102, thereby implementing parts other than the functions implemented by the communication interface 103 in the time synchronization unit 33, the reception monitoring unit 34, the frame receiving unit 31, and the frame transmitting unit 32.

[0048] The above program can be provided to the user in a state pre-stored in the storage device 102, or can be supplied to the user in a state written to a recording medium readable by a computer or the like, such as a CD (Compact Disc)-ROM, a DVD (Digital Versatile Disc)-ROM, etc., and installed by the user in the storage device 102.

[0049] As described above, according to this embodiment, in the communication system 4 connected to the switching hub 2 that does not support IEEE 1588, the slave synchronizing stations 3a and 3b that perform time synchronization start the reception monitoring timer 340 when sending the DelayReq message. The timeout setting value of the reception monitoring timer 340 is set to tO, the number of connections of the slave synchronizing stations 3a and 3b connected to the switching hub 2 is set to N, the transmission period of the DelayReq message of the slave synchronizing stations 3a and 3b is set to T, and it is set that tO ≤ T / N. When the slave synchronizing stations 3a and 3b do not receive the DelayResp message from the master synchronizing station 1 within the timeout setting value tO, the DelayReq message is retransmitted. When the slave synchronizing stations 3a and 3b complete the measurement of the transmission delay time through the retransmitted DelayReq message, the DelayReq message is sent at intervals of the transmission period T from the time when the DelayReq message is retransmitted. Thus, in the communication system 4 in which a plurality of requesters, that is, the slave synchronizing stations 3a and 3b, are connected to the switching hub 2 that does not support IEEE 1588, the slave synchronizing stations 3a and 3b can also measure the transmission delay time and can perform time synchronization.

[0050] Embodiment 2.

[0051] In Embodiment 2, the requester, that is, the slave synchronizing station, counts the number of connections N and automatically calculates the timeout setting value tO. The parts different from Embodiment 1 will be described.

[0052] Figure 7 FIG. is a structural example diagram of the communication system 4A according to Embodiment 2. The communication system 4A includes a master synchronizing station 1, a switching hub 2, and slave synchronizing stations 3Aa and 3Ab that are synchronized with the master synchronizing station 1. In Figure 7 In the shown communication system 4A, the slave synchronizing stations 3Aa and 3Ab are requesters for measuring the transmission delay time of the transmission path between them and the master synchronizing station 1, and the master synchronizing station 1 is the responder.

[0053] In addition, depending on the structure of the communication system, the slave synchronizing station may sometimes be the responder. Figure 8 FIG. is a structural example diagram of the communication system 4Aa according to Embodiment 2. The communication system 4Aa includes a master synchronizing station 1, a switching hub 2, a slave synchronizing station 3Ac, and slave synchronizing stations 3Aa and 3Ab that are synchronized with the slave synchronizing station 3Ac. In Figure 8 In the shown communication system 4Aa, the slave synchronizing stations 3Aa and 3Ab are requesters for measuring the transmission delay time of the transmission path between them and the slave synchronizing station 3Ac, and the slave synchronizing station 3Ac is the responder. In Figure 8In the communication system 4Aa shown, the slave clock 3Ac can measure the transmission delay time of the transmission path between the slave clock and the master clock 1 according to the IEEE 1588 process. In the present embodiment, Figure 7 the communication system 4A shown will be described as an example.

[0054] The structures of the slave clocks 3Aa and 3Ab will be described. Figure 9 FIG. is a diagram showing a structural example of the slave clock 3Aa according to Embodiment 2. Since the slave clocks 3Aa and 3Ab have the same structure, the slave clock 3Aa will be described as an example. The slave clock 3Aa includes a frame receiving unit 31A, a frame transmitting unit 32, a time synchronization unit 33, and a reception monitoring unit 34A.

[0055] The frame receiving unit 31A is a receiving unit including a frame parsing unit 310A, a table management unit 311A, and a counter 312A.

[0056] The frame parsing unit 310A parses the frame received from the switching hub 2. When the received frame is a message associated with time synchronization, the frame parsing unit 310A outputs the received data included in the received frame to the time synchronization unit 33. When the slave clock 3Aa is a requester, if the frame parsing unit 310A receives a DelayResp message targeted at the slave clock 3Aa among the messages associated with time synchronization, the frame parsing unit 310A notifies the reception monitoring unit 34A of the reception of the DelayResp message. If the frame parsing unit 310A receives a DelayReq message sent from another requester, i.e., the slave clock, among the messages associated with time synchronization, the frame parsing unit 310A notifies the table management unit 311A of the requester identification information indicating the slave clock as the transmission source included in the DelayReq message. The requester identification information is, for example, a MAC (Media Access Control) address or the like.

[0057] When the slave clock 3Aa is a responder, if the frame parsing unit 310A receives a DelayReq message among the messages associated with time synchronization, the frame parsing unit 310A saves the timestamp value at the reception time point. The frame parsing unit 310A notifies the frame transmitting unit 32 of the following information: the received timestamp value, the transmission source information of the DelayReq message indicating the transmission source, i.e., the requester, included in the DelayReq message, and the DelayReq message.

[0058] The table management unit 311A registers the requester identification information notified from the frame analysis unit 310A in the requester table that the table management unit 311A has. When the requester identification information is newly registered in the requester table, the table management unit 311A increments the count of the counter 312A by 1. The initial value of the count value of the counter 312A is 1. Regarding the requester identification information registered in the requester table, when the table management unit 311A does not receive the same requester identification information notified from the frame analysis unit 310A within a specified time, the table management unit 311A deletes the corresponding requester identification information from the requester table and decrements the count of the counter 312A by 1.

[0059] The frame analysis unit 310A or the table management unit 311A notifies the reception monitoring unit 34A of the count value of the counter 312A. Thus, in the synchronization slave station 3Aa, the frame reception unit 31A counts the connection number N of the synchronization slave stations that are the requesters connected to the switching hub 2 based on the reception number of DelayReq messages sent by other requesters, i.e., the synchronization slave stations.

[0060] The reception monitoring unit 34A has a reception monitoring timer 340A and a timeout value setting unit 341A.

[0061] The timeout value setting unit 341A calculates the timeout setting value tO of the reception monitoring timer 340A using the count value of the counter 312A notified from the frame reception unit 31A. Specifically, the timeout value setting unit 341A sets the count value of the counter 312A as the connection number N and calculates the timeout setting value tO of the reception monitoring timer 340A so that tO ≤ T / N. The timeout value setting unit 341A notifies the calculated timeout setting value tO of the reception monitoring timer 340A to the reception monitoring timer 340A.

[0062] The reception monitoring timer 340A is a timer for monitoring the reception of DelayResp messages. The timeout setting value tO of the reception monitoring timer 340A is the value notified from the timeout value setting unit 341A.

[0063] Thus, the reception monitoring unit 34A calculates the timeout setting value tO using the connection number N counted by the frame reception unit 31A and the transmission period T.

[0064] Next, the operations of the synchronization slave stations 3Aa and 3Ab will be described. Figure 10 This is a flowchart showing the operation of the reception monitoring unit 34A of the synchronization slave station 3Aa according to Embodiment 2 for calculating the timeout setting value tO. Since the synchronization slave stations 3Aa and 3Ab perform the same operations, the synchronization slave station 3Aa will be taken as an example for description.

[0065] In the reception monitoring unit 34A, the timeout value setting unit 341A acquires the count value of the counter 312A from the frame reception unit 31A (step S41). The timeout value setting unit 341A sets the count value of the counter 312A as the connection number N, and uses the connection number N and the transmission period T of the transmission period timer 320 of the frame transmission unit 32 to calculate the timeout setting value tO that satisfies tO ≤ T / N (step S42). The timeout value setting unit 341A notifies the calculated timeout setting value tO to the reception monitoring timer 340A (step S43). Since the monitoring operation of the reception monitoring unit 34A using the timeout setting value tO is the same as the monitoring operation of the reception monitoring unit 34 in the first embodiment shown in Figure 4 , the detailed description is omitted.

[0066] Regarding the synchronous slave station 3Aa, similar to the synchronous slave station 3a in the first embodiment, it is implemented by the hardware structure shown in Figure 6 .

[0067] As described above, according to this embodiment, the synchronous slave stations 3Aa and 3Ab calculate the connection number N of the requesting party connected to the switching hub 2 based on the number of DelayReq messages received from other synchronous slave stations, and use the connection number N to calculate the timeout setting value tO of the reception monitoring timer 340A. Thus, the synchronous slave stations 3Aa and 3Ab can automatically calculate the timeout setting value tO of the reception monitoring timer 340A. As a result, the user does not need to calculate and change the timeout setting value due to the difference in the structure of the communication system 4A, and can easily operate the communication system 4A.

[0068] The structure shown in the above embodiment represents an example of the content of the present invention, and it can also be combined with other known technologies, and within the scope not departing from the gist of the present invention, a part of the structure can also be omitted or changed.

[0069] Description of reference numerals

[0070] 1 Synchronous master station, 2 Switching hub, 3a, 3b, 3c, 3Aa, 3Ab, 3Ac Synchronous slave stations, 4, 4a, 4A, 4Aa Communication systems, 31, 31A Frame reception units, 32 Frame transmission unit, 33 Time synchronization unit, 34, 34A Reception monitoring units, 310, 310A Frame analysis units, 311A Table management unit, 312A Counter, 320 Transmission period timer, 330 Time counter, 340, 340A Reception monitoring timers, 341A Timeout value setting unit.

Claims

1. A time synchronization device, which is the first device. The first device measures the transmission delay time between the second device via a relay device capable of connecting multiple first devices. The time synchronization device is characterized by comprising: A sending unit that sends a request message for measuring the transmission delay time to the second device; A receiving unit that receives a response message from the second device, which is a response to the request message; And A receiving monitoring unit that has a receiving monitoring timer. When the sending unit sends the request message, the receiving monitoring timer is started. When the receiving monitoring timer times out before the receiving unit receives the response message, an instruction to immediately re - send the request message is sent to the sending unit. Set the timeout setting value of the receiving monitoring timer as tO, set the number of connected time synchronization devices to the relay device as N, and set the sending period of the request message of the sending unit as T, where tO ≤ T / N. When the receiving unit receives the response message before the receiving monitoring timer times out, the sending unit sends the request message at the sending period of T. The sending unit has a sending period timer, and the sending period timer is a timer that times out at the same sending period as the sending period timers of other time synchronization devices. When the request message is re - sent due to the timeout of the receiving monitoring timer, the sending period timer restarts. When the receiving unit receives the response message before the receiving monitoring timer times out after the re - sending of the request message, the sending unit sends the request message when the sending period timer that has restarted times out.

2. The time synchronization device according to claim 1, characterized in that The sending unit counts the number of connected time synchronization devices to the relay device according to the number of received request messages sent by other time synchronization devices. The receiving monitoring unit calculates the timeout setting value using the number of connected time synchronization devices counted by the receiving unit and the sending period.

3. A communication system, characterized in that, Comprising: The time synchronization device according to claim 1 or 2, that is, the first device; A relay device capable of connecting multiple first devices; and A second device that, when receiving a request message for measuring the transmission delay time sent from the first device, sends a response message, which is a response to the request message.

4. A time synchronization method, which is a time synchronization method of a time synchronization device. The time synchronization device is the first device. The first device measures the transmission delay time between the second device via a relay device capable of connecting multiple first devices. The time synchronization method is characterized by comprising: A sending step in which a sending unit sends a request message for measuring the transmission delay time to the second device; A receiving step in which a receiving unit receives a response message from the second device, which is a response to the request message; and Monitoring step, the receiving monitor has a receiving monitor timer, which is started when the sending unit sends the request message. When the receiving monitor timer times out before the receiving unit receives the response message, an instruction to immediately retransmit the request message is sent to the sending unit. Set the timeout setting value of the receiving monitor timer to tO, set the number of connections of the connection synchronization device connected to the relay device to N, and set the sending period of the request message of the sending unit to T, where tO ≤ T / N. When the receiving unit receives the response message before the receiving monitor timer times out, the sending unit sends the request message at the sending period of T. The sending unit has a sending period timer, which is a timer that times out at the same sending period as the sending period timers of other time synchronization devices. The time synchronization method further includes the following steps: When the request message is retransmitted due to the timeout of the receiving monitor timer, the sending period timer is restarted; and When the receiving unit receives the response message before the receiving monitor timer times out after the retransmission of the request message, the sending unit sends the request message when the sending period timer that has been restarted times out.

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